Project Summary/Abstract Objective/Hypothesis. Microbial keratitis is a rapidly progressing, sight-threatening infection of the cornea. Currently, treatment of microbial keratitis primarily focuses on the pathogen versus the host response. While control of the bacteria is of utmost importance, antibacterial treatment does not guarantee good visual outcome. Treatment with corticosteroids does address the host response to an extent; however, there remains indecision regarding the use of this class of hormones due to the immunosuppressive side effects. We are investigating an endogenous protein, thymosin beta-4 (T?4), which can be used as an adjunct to antibiotics to more effectively treat this visually debilitating disease. Our goal is to understand how T?4 promotes resolution of inflammation ? an aspect of the disease that has yet to be adequately addressed by current treatments. Further, we will determine its clinical applicability as an adjunct therapy against multiple pathogens known to cause microbial keratitis, including multi-drug resistant strains. Given that microbial keratitis results in over 1 million combined office/outpatient and emergency visits annually with the cost of treatment estimated at $175 million per year in the US alone, these studies are relevant to human health and have considerable medical and economic impact. Specific Aims. This proposal intends to: 1) ascertain the mechanisms of T?4 on inflammation-resolution and enhanced host defense; and 2) establish the efficacy of T?4 as an adjunct treatment with antibiotic for microbial keratitis against multiple pathogens. Study Design. This proposal implements both in vivo and in vitro studies using a number of well- established techniques to examine the mechanistic and therapeutic effects of T?4. In vivo studies include use of transgenic mice, and both P. aeruginosa- and S. aureus-induced infections, including clinical isolates that are antibiotic resistant. Further, we extend beyond infectious keratitis and utilize a sterile keratitis model. Restoration of corneal structure and function will be assessed, as well. In vitro studies are designed to complement the in vivo models; all of which focuses on T?4's effect on immune-resolution and enhanced host defense, ultimately leading to restoration of corneal structure and function. Impact. Overall, the studies proposed seek to provide preclinical evidence for the development of a novel, potent immunoresolvent exhibiting significant impact on treatment for ocular infectious disease that is devoid of deleterious immunosuppressive side effects.